1. Field of the Invention
The present invention relates to a Computer Aided Manufacturing System (CAM) system which aides determining a work-location to be machined and machining steps for manufacturing the work, more particularly, and to CAM and method for machining a plurality of locations to be machined, which are extracted from a three-dimensional CAD model, in optimum postures (setups) and optimum machining steps (machining sequence).
2. Description of the Related Art
A two- or three-dimensional Computer aided design (CAD) and CAM system is utilized in a process of product development from product design to manufacturing. In the process of product development, design of a product is first performed in the design department by using a three-dimensional CAD apparatus through dialog with a designer, whereby a three-dimensional CAD model (product model) representing a product shape is formed. Three-dimensional CAD data prepared in that stage is transferred to a three-dimensional CAM apparatus through an interface based on a universal data exchange format, such as Initial Graphics Exchange Specification (IGES) or Standard for the exchange of product model (STEP). In addition, the designer converts the product shape to two-dimensional drawings (design drawings) by using the three-dimensional CAD apparatus and writes additional information, e.g., dimensions, machining methods such as spot-facing and drilling, and surface roughness, on the two-dimensional drawings.
On the other hand, the three-dimensional CAM apparatus receives the three-dimensional CAD data from the three-dimensional CAD apparatus and enters additional information, such as locations to be machined, machining methods, and surface roughness, into the three-dimensional CAD data through dialog with a manufacturing engineer while referring to the two-dimensional drawings. Further, the three-dimensional CAM apparatus obtains developed data of the product, etc. from the three-dimensional CAD data added with attribute information, such as locations to be machined, machining methods, and surface roughness, calculates a tool/machining path (tool locus data) in an NC working machine based on the developed data, and prepares NC data to perform NC machining.
When the NC data is prepared in such a two- or three-dimensional CAD and CAM system, the manufacturing engineer takes into account machining methods such as drilling, used tools, machining conditions (such as a tool rotating speed), a table moving speed, a cut amount, etc., for each of individual locations to be machined, and sets those items of information for the three-dimensional CAM apparatus through dialog, thereby forming the machining path.
Generally, the machined location in the three-dimensional CAD model formed by utilizing the CAD apparatus includes recognition of in what way what shape is arranged with respect to a basic shape of the three-dimensional CAD model (i.e., a machining shape feature: hereinafter referred to as a “machining feature”). When the three-dimensional CAD data is transferred from the CAD apparatus to the CAM apparatus, the geometrical shape of the product model is transferred to the CAM apparatus. At that time, however, the attribute information of each machining feature is not recognized by the CAM apparatus and is lost. In view of such a problem, some of recent CAM apparatuses capable of handling the three-dimensional CAD data have the function of automatically recognizing the machining feature from the geometrical shape of the product model and automatically selecting proper ones of machining tools and machining conditions which are registered in advance, thereby forming the machining path. Japanese Unexamined Patent Application Publication No. 6-31589 discloses a method of generating NC data that is applicable to operate that type of CAM apparatus.    [Patent Document 1] Japanese Unexamined Patent Application Publication No. 6-31589
When one part is machined, the part usually may have a plurality of or plural kinds of locations to be machined. Machining of those locations to be machined requires setups for setting a plurality of machining postures, change of the machining sequence to avoid useless consumption of a machining time, and re-preparation of the machining feature information.
The known CAM apparatus is able to automatically recognize the machining feature from the geometrical shape of the product model, to identify hole shapes such as a countersink and a counterbore (spot-faced hole), and to decide a machining posture from the center axis or the opening direction of a hole. However, because the actual product shape includes a shape for which the machining posture is not uniquely decided (see FIG. 18), and a special shape for which the machining feature is not uniquely decided (see FIG. 19), the machining posture and the machining feature are finally changed or corrected through dialog in the CAM apparatus at the human's discretion. For that reason, the known CAM apparatus is not yet sufficiently satisfactory in that a new problem arises with the change and disables subsequent processing or forms an erroneous machining path, thus causing an incorrect result.
FIG. 18 shows a cross section in which a simple through hole 1002 is bored in a part 1000. FIG. 18 represents the case where the machining posture is not uniquely decided because there are two kinds of machining directions from above and below (shown by arrows A and B). FIG. 19A represents a cross section of an example 1110 in which a blind hole is divided into three holes 1130, 1140, 1150 at its intermediate portions due to a specific product shape, and FIG. 19C represents a cross section of an example 1210 in which blind holes 1230, 1240, and 1250 are divided by another hole 1260. The blind holes in FIGS. 19A and 19B should be each identified as one blind hole 1180 and 1230-1250 as shown in FIGS. 19B and 19D, respectively, but they are recognized just as holes opened in a reference face in many cases. When the divided hole is recognized as one simple hole, a useless machining time is consumed depending on the machining sequence of the divided holes. For example, when a horizontal hole is first machined in (c), idle machining feed is generated in a space dividing a vertical hole when the vertical hole is machined.